The overall goal of this research is to use our unique mouse models of Types A & B Niemann-Pick disease (NPD) to develop new therapies for this disorder and to uncover novel pathogenic mechanisms. Two aims are proposed. Aim 1: Preclinical Evaluation of Two New Therapies. In the first set of studies we will evaluate a novel enzyme enhancement approach using the heat shock protein, Hsp70. These experiments are based on a recent publication showing that Hsp70 enhanced residual ASM activity and reduced lysosomal pathology in cells from Type A and B NPD patients, a finding that has been supported by new in vivo data obtained since the previous submission. The second set of studies will continue our work aimed at improved delivery of ASM to the lung using ICAM-1. A proof-of-principle gene transfer experiment will be undertaken that will use AAV8 vectors to express ASM/ICAM-1 fusion proteins in the livers of NPD mice. Uptake and efficacy of the fusion enzymes in the lung and other clinically important organs will be studied. New in vivo data also has been obtained to demonstrate the feasibility of this approach. Aim 2: Investigation of Novel Pathogenic Mechanisms Leading to ERT-Related Liver Toxicity. Preclinical ERT studies in ASM knockout (ASMKO) mice have shown that administration of recombinant ASM at doses above 5 mg/Kg results in liver bleeding, the release of liver enzymes, and death. We have recently found that sphingosine, not sphingomyelin, is the major accumulating lipid in the livers of these mice, and hypothesize that sphingosine storage is responsible, at least in part, for the ERT-associated toxicity. We will determine the source of accumulating sphingosine by evaluating the expression of ceramidases, sphingosine kinases and sphingosine-1-phosphate lyase in the ASMKO mice, and breed these animals to mice lacking sphingosine kinase-1 to determine the effects on ERT- associated liver toxicity. These results should provide a mechanistic basis for the clinical observations in the mice, and also may lead to new strategies to overcome this toxicity.